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It almost sounds like something might have changed in your water supply that caused them stress. Maybe ammonia in the water supply (as already suggested) or something that effected the TDS level which could have effected the pH stability.

Just a few guesses on my part tho.

If you take your time to do the research FIRST, you can successfully set-up and keep ANY type of aquarium with ease."Not using a quarantine tank is like playing Russian roulette. Nobody wins the game, some people just get to play longer than others." - Anthony CalfoFishless CycleCycling with FishMarine Aquarium Info [URL="http://saltwater.aquaticcommunity.com/"]

Brhino! Oh man im so sorry. It almost sounds like it has to be the source water that had something added. Temp drop and raise can really affect loaches negatively but I can imagine you would put it in so cold as to shock a cold water fish... Did you check your heater for a potential electrical current? It may be weak and only affected the two fish... Agree with lady hobbs to check the A/N/N levels over the next few days in case you did forget prime... Im so sorry man!

50% water change weekly is a huge change. Is it your nitrate level (over>50) that makes you perform such huge changes? If so, then good alternative wouild be making 20% change twice a week. In case nitrates don't go that high, I suggest that you make 20% change a week.

50% water change weekly is a huge change. Is it your nitrate level (over>50) that makes you perform such huge changes? If so, then good alternative wouild be making 20% change twice a week. In case nitrates don't go that high, I suggest that you make 20% change a week.

Allesgut,
the minimum recommend amount, regardless of your nitrate level, is 50%.
I've done 50% water changes weekly, if not 2x a week for the past year. Never lost a fish due to it.

In nature, fish have "constant" water changes, the more we mimic that, the happier they are.
20% weekly isn't helping anything.

Allesgut,
the minimum recommend amount, regardless of your nitrate level, is 50%.
I've done 50% water changes weekly, if not 2x a week for the past year. Never lost a fish due to it.

In nature, fish have "constant" water changes, the more we mimic that, the happier they are.
20% weekly isn't helping anything.

Recommended by who? Plenty of people do 10-40% water changes (depending on the bioload). And also, doing multiple smaller water changes throughout the week as Allesgut suggested is better because it keeps the water more consistent and will be less stressful on the fish (as you even said, in nature fish get constant water changes; they don't get a huge water change at the end of every week...).

Recommended by who? Plenty of people do 10-40% water changes (depending on the bioload). And also, doing multiple smaller water changes throughout the week as Allesgut suggested is better because it keeps the water more consistent and will be less stressful on the fish (as you even said, in nature fish get constant water changes; they don't get a huge water change at the end of every week...).

recommended by any experienced fish keeper...look at any thread here and people are saying do more/bigger pwc, cleaner water helps more than most meds. i'm not debating the more than once a week pwc, i'm talking 20 vs 50 at the end of the week.

if you are stressing out your fish during a pwc, then you are doing it wrong.

there is no reason not to do at least 50percent weekly at the minimum. if you cant haul the buckets, get a water change system.

To get back on topic-the OP does 50percent and that isn't the issue. the issue has to be in the water company changing up things, or a freak accident, or who know. but 20 vs 50percent isn't going to kill a fish.

I think it would be safe to say there are many different approaches to getting and keeping a healthy tank. Some people have great results with 20% to 40% weekly water changes, others (like myself) have been having great success for many years with 50% and higher weekly water changes. Many discus owners also complete a lot more water changes that that. The are rules of thumb, but no hard fast rules for success.

I'm sure Brhino is changing the correct amount of water for his set-up as he is a experienced keeper who has just experienced a unfortunate set-back.

If you take your time to do the research FIRST, you can successfully set-up and keep ANY type of aquarium with ease."Not using a quarantine tank is like playing Russian roulette. Nobody wins the game, some people just get to play longer than others." - Anthony CalfoFishless CycleCycling with FishMarine Aquarium Info [URL="http://saltwater.aquaticcommunity.com/"]

Considering Brhino has like 100 danios and 8 growing loaches, 50% is a great amnt of water to change. There are a lot of methods and lets just be blunt here in saying Brhino is one of our best on this site at keeping a healthy tank. I dont doubt his method of changing water in a tank. And in 45 min I cant see chlorine or cold shock to be an issue for fish.